1. Field of the Invention
The present invention relates to an operable angle adjusting structure for a wiper for wiping windshield surfaces of motor vehicles such as automobiles, buses and trucks.
2. Description of the Related Art
Generally, a wiper has a wiper arm that is driven by a motor to reciprocally swing for wiping a windshield surface. It is desirable for a wiper to have a greater wiping angle for providing a wider field of view. The wiping angle of a wiper arm is determined by an axis-to-axis distance between an axis of a turnable shaft at a proximal end side of a link member and a center axis of a ball joint at a distal end side thereof, the link member being disposed in a power transmission path extending from a motor to a wiper shaft. The longer the axis-to-axis distance, the greater the wiping angle. From this standpoint, it is desirable to set the axis-to-axis distance so that the wiping angle is maximized. Due to manufacturing errors caused when machining and mounting the turnable shaft and the ball joint to the link member, however, the wiping angle may exceed the maximum axis-to-axis distance. This raises a problem that the wiping angle of the wiper arm is increased to such an extent so as to interfere with a pillar.
The above problem can be avoided by employing special precision machining which provides higher accuracy than usual, when machining and mounting the turnable shaft and the ball joint to the link member, or by shortening the axis-to-axis distance in anticipation of the manufacture errors. However, the former method has poor production efficiency and requires a special precision machining apparatus, thus increasing the equipment cost. On the other hand, the latter method is free from the problems of the former method, but the wiping angle is necessarily reduced.
An opposing type wiper comprises a crank arm rotatably driven by a motor, an intermediate link pivotally supported at a middle position, and a connecting rod disposed between the crank arm and the intermediate link for converting a rotating motion of the crank arm into a reciprocal swing motion of the intermediate link. Further, upper and lower ends of the intermediate link are connected respectively to right and left wiper shafts via drive rods, causing right and left wiper arms to be operated for wiping the windshield surface in oppositely moving relation. Additionally, changes in angular speeds of the right and left wiper arms are set to be asymmetrical therebetween so that wiper blades of the right and left wiper arms are overlapped with each other in their lower inverting positions. Specifically, the right and left wiper blades are laid one above the other without interfering with each other, by setting the angular speed of the overlying wiper arm (on the side of a driver's seat) to be larger than that of the underlying wiper arm (on the side of an assistant's seat) in the vicinity of the lower inverting positions.
Thus, the opposing type wiper includes many components, and even a small error significantly affects the wiping angle and often leads to a risk that the wiper arms may interfere with each other. Also, because the angular speeds of the wiper arms are intentionally made different between the driver's side and the passenger's side, high accuracy is required in setting of the components and setting errors result in a significant influence.